1. Field of the Invention
The invention relates to internal combustion engine fuel injectors having a replaceable control module.
2. Background Art
An example of a fuel injector pump and control valve assembly of known design is shown in U.S. Pat. No. 6,238,190, as well as U.S. Pat. No. 6,276,610. These patents, which are assigned to the assignee of the present invention, disclose a fuel injection pump and valve assembly that comprises a relatively large and complex pump body having a precision-machined pumping chamber and a control valve chamber. The pumping chamber is defined by a pumping cylinder and an engine camshaft-driven piston in the cylinder. A fuel inlet supplies fuel to the pumping chamber. An outlet port communicates with a high-pressure fuel delivery passage extending through the control valve for delivering pulses of pressurized fluid to the nozzle and a nozzle needle valve. The piston, which usually is described as a pump plunger, reciprocates in the pumping cylinder as it is mechanically driven with a pumping stroke frequency directly related to engine speed. A fuel control valve in the control valve chamber establishes and disestablishes fuel delivery from the high-pressure pumping chamber to the nozzle. The control valve is controlled by a solenoid actuator that responds to control current pulses in a driver circuit for an electronic engine control system. The shape of pressurized fuel pulses delivered to the nozzle is under the control of the fuel control valve.
An injector assembly of known design is supplied with fuel from a fuel supply pump, which operates at a relatively low inlet fuel pressure. The fuel circulates continuously through the fuel control valve, the latter being under the control of a control solenoid actuator.
The control valve is movable between open and closed positions. The stroke of the control valve is within a range that includes a rate shape position between the open position and the closed position.
If the operating requirements for the engine with an injector assembly should change, it is necessary to use a different injector assembly. It is not possible to modify independently the operating characteristics by substituting one control valve for another or one stator assembly for another, for example, without replacing the entire assembly.
Furthermore, high volume manufacturing operations for known injector assemblies are characterized by a relatively high scrap rate because it usually is necessary to discard an entire injector assembly if one of its elements or subassemblies is defective or is out-of-tolerance.
The cost of manufacture for known injector assemblies is increased by the precision machining operations that are required during their manufacture. The starting material for forming the injector pump body, for example, is usually a forging that requires a substantial finish machining prior to assembly of the various components of the injector assembly.
It is an objective of the invention to provide an injector assembly for an internal combustion engine, such as a diesel engine, wherein the essential elements of the injector are formed in separate subassemblies that can be interchanged with other subassemblies without affecting companion subassemblies. This makes it possible to reduce the rate of scrap during high-volume manufacture of injectors. It is an objective also to reduce the cost of manufacture and the cost of materials used during manufacture by reducing the need for finish machining and by reducing the number of assembly steps for the various components. These objectives are achieved in part with the design of the present invention by providing an injector pump body that can be machined using bar stock rather than a forging.
A control module and a stator assembly for the control module are formed as separate elements that can be interchanged with control modules and stator assemblies having different characteristics without affecting the other elements of the assembly. The stator assembly and the control module can be assembled together with a pump body and a nozzle valve and spring subassembly using a simplified assembly technique, which uses a nozzle nut as a clamping element that can be threaded on the cylinder body. The nozzle nut contains a nozzle valve and the control module so that the elements of the injector assembly can be held together in sealing engagement without the requirement for special fasteners or seals.
The injector assembly is characterized by its reduced packaging size as well as its ease of manufacture and reduced manufacturing cost.
The nozzle assembly includes a spring cage for a nozzle valve spring, which engages a nozzle needle valve. A nozzle orifice is opened and closed by the needle valve. The control module has a body with a control valve chamber, which receives a control valve element. An electromagnetic coil actuator in the module body has an armature connected to the control valve element.
A first high-pressure passage is formed in the injector plunger pump body, a second high-pressure passage is formed in the module, and a third high-pressure passage is formed in the spring cage and in the nozzle body, the latter communicating with the discharge orifice as pressure in the third high-pressure passage shifts the needle against the force of the needle valve spring.
The module and the injector pump body have planar surfaces and an interface, whereby the first and second high pressure passages are in communication. The module and the spring cage also have planar surfaces that define another interface, whereby the second and third high-pressure passages are in communication. The module, the nozzle subassembly and the injector pump body are installed in independent, adjacent, stacked relationship as the nozzle nut is connected to the injector plunger pump body.